In a vehicle air conditioner described in JP Patent No. 2540738, a super-heat vapor generated by exhaust heat of an internal combustion engine (referred to as engine) is supplied to a compressor, and the compressor is operated as an expansion device, so that power is recovered from the exhaust heat. When a vapor-compression refrigerant cycle is operated in summer, the compressor is not operated as the expansion device, and power cannot be recovered from the exhaust heat of the vehicle.
By contrast, in a combined cycle system described in JP-A-55-99561, a Rankine cycle for recovering power from exhaust heat is provided separately from a vapor-compression refrigerant cycle, and the power recovered in the Rankine cycle is supplied to a compressor of the vapor-compression refrigerant cycle. Therefore, the Rankine cycle and the vapor-compression refrigerant cycle can be operated at the same time. However, in this case, a radiator (condenser) for the vapor-compression refrigerant cycle and a condenser for the Rankine cycle need to be provided, and a large mounting space for mounting both of the radiator and the condenser is required. Therefore, it is difficult for the combined cycle system to be mounted in a small mounting space.
Generally, a condensation pressure in the Rankine cycle is higher than a pressure of the high-pressure side refrigerant in the vapor-compression refrigerant cycle. Thus, when the radiator of the vapor-compression refrigerant cycle and the condenser of the Rankine cycle are commonly used while the same kind of fluid as the refrigerant of the vapor-compression refrigerant cycle is used as a circulation fluid of the Rankine cycle, the pressure of the high-pressure side refrigerant of the vapor-compression refrigerant cycle increases to approach to the condensation pressure of the Rankine cycle. Therefore, a discharge pressure of the compressor is increased, and power consumption in the compressor is increased. As a result, the coefficient of performance of the vapor-compression refrigerant cycle is deteriorated, and sufficient cooling capacity may be not obtained in the vapor-compression refrigerant cycle when the vapor-compression refrigerant cycle is used as a vehicle air conditioner.